1. Field of the Invention
The present invention relates to a variable displacement wobble plate type compressor. More particularly, it relates to an improvement in the guide means for a wobble plate of a variable displacement wobble plate type compressor.
2. Description of the Related Art
A typical variable displacement wobble plate type compressor to be used in a vehicle airconditioning compressor is disclosed in U.S. Pat. No. 4,428,718 to T. J. Skinner. In this compressor, a non-rotating ring shaped wobble plate capable of angulating for causing a reciprocating motion of pistons is supported by a rotatable drive plate, via a thrust needle bearing, and is axially slidably guided by an axially extended guide pin, via a ball guide. The guide pin is press-fitted at opposite ends in a cylinder block having a plurality of cylinders and a crankcase defining therein a chamber for retaining the wobble plate and the drive plate on an axial drive shaft which is operatively connected, at an outer end, to a car engine. The ball guide is retained between semi-cylindrical guide shoes which are slidably mounted for reciprocal radial movement in the wobble plate. The detailed construction of the guide mechanism for the wobble plate of the above-mentioned variable displacement compressor is definitely disclosed in U.S. Pat. No. 4,297,085 to B. L. Brucken. Particularly, FIGS. 3 through 5 of the latter U.S. Patent clearly illustrate the constructional relationship among the guide pin, the ball guide, and the semi-cylindrical guide shoe members. In this connection, it is stated that each of the guide shoe members has a concave semi-spherical recess which is formed in a planar surface of its guide shoe members, respectively, and that each planar surface defines a planar portion, bearing substantially slidably on the guide pin, operative to maintain the guide shoe members in substantially parallel planes. It is true that this construction is able to ensure a stable wobble motion of the wobble plate, but, since each of the above-mentioned planar portions of the shoe members must always slide on the surface of the guide pin while maintaining a substantial point to point contact therebetween, the contact portions of the guide pin and the shoe members must become worn during long-term operation of the compressor. Therefore, it is necessary to lubricate the guide mechanism for the wobble plate, although U.S. Pat. No. 4,297,085 is silent about lubrication of the wobble plate guide mechanism. As a result, the conventional guide mechanism lacks durability in operation.